Bleaching cellulosic materials



n-iutsat Virginia No Drawing. Filed Feb. 29, 1960, Ser. No. 11,488 6Claims. (Cl. 8-108) This invention relates to improvements in bleachingusing aqueous solutions of chlorites.

In the bleaching of cellulosic textiles, an acid solution of a chloritegives maximum bleaching with minimum degradation and the production ofgoods of high whiteness and full strength. A typical bleach bathcontains, for example, approximately one gram per liter of sodiumchlorite. Sutficient acid is added to the bath with or without bufferingto bring the pH to the desired value, generally to a pH of about 3.5 forcotton goods. Acetic acid is the preferred acid for achieving the pH of3.5 and formic acid is the preferred acid for solutions of lower pH.Mineral acids, including sulfuric acid and phosphoric acid, are alsofrequently used as acidifying agents. Buffer salts, for example, Na i-IPNaH PO or NHJ-IF can be added. In addition, wetting agents which areeffective under acid conditions, for example, the Igepons (salts ofacylalkyl taurides) are commonly added. Bleaching baths of thesecompositions are commonly used at elevated temperatures, for example,180 F. to 195 F.

Under these conditions of use, the bleaching solutions generate chlorinedioxide rather rapidly, as evidenced by the development of a yellowcolor in the solution and by the evolution of chlorine dioxide as a gasfrom the surface of the solution. This generation of chlorine dioxide isobjectionable in that the gas lost from the solution represents a lossin bleaching power. It is also objectionable as a health hazard whensufficient chlorine dioxide is evolved to affect workers deleteriously.Chlorine dioxide is an irritating gas and requires removal, for exampleby means of hoods, from the working space. Furthermore, acid chloritesolutions, particularly when chlorine dioxide is being evolved in therange of pH 2 to pH 4, are corrosive to stainless steels and othermetals. These metals become pitted and then corrode at a faster ratethan the original highly polished surfaces. In addition, the corrosionproducts in the solution frequently stain the textile and acceleratefurther decomposition of the chlorite to chlorine dioxide. Thus, it isnecessary, for the most economical and eflicient bleaching, to acidifythe bleaching bath to form chlorous acid and/or chlorine dioxide at arate matching the demand on the solution by the textile being bleachedand, at the same time, to avoid producing an excess of chlorine dioxidewhich would saturate the solution and be evolved as a gas.

Fine adjustment of the pH of the bleaching bath is difficult, and byitself, is inadequate to provide sufiicient chlorine dioxide, as opposedto too much chlorine dioxide. Control of the rate of formation ofchlorine dioxide has been attempted by starting the bleach at a moderatetemperature, such as 160 F. and a moderate pH of about 4 and adding acidand increasing the temperature during the bleaching period to activatethe remaining chlorite more strongly. But such procedures requireconstant manual attention and it is more desirable, in any event, to addsufficient acid at the beginning for the entire process and to maintainconstant temperature.

Considerable control of the corrosion aspect of the excessive chlorinedioxide production problem can be effected by addition to the bleachingbath of nitric acid as the acidifying agent or the addition to thebleaching SEARCH RUOiiti Ere bath of inorganic nitrates up to a molarratio of 0.5:1 or more of nitrate to chlorite. For some fabrics, such asDacron (polyethylene terephthalate fiber), the use of nitric acid ornitrates has been specified by the manufacturer when chlorite bleachingis employed. Many textile plants, however, regard nitric acid asdangerous to handle. Moreover, control of pH using nitric acid isdifiicult, since it has no buffering action. Consequently, some millshave preferred to add nitrate salts, e.g., sodium nitrate, to the bathalong with the other ingredients and to employ acetic acid as theacidifying agent. Acetic acid has a pronounced and useful bufieringaction, tending to hold the pH value somewhat constant or, at least,minimizing its rise as the bleach bath is used. The addition of sodiumnitrate or other nitrate salts to the bath does not interfere with thebuffering action. However, there is .a limit to the ability of nitratesto retard corrosion of stainless steel in acidified chlorite solutions;to reduce the amounts of corrosion products, particularly iron compoundswhich cause the decomposition of the chlorite and the production ofchlorine dioxide; and to overcome the adverse eifects of, for example,iron which may be introduced into the bleach bath from other sources.

One method for lessening the corrosiveness of chlorite baths is toactivate the chlorite with formaldehyde, for example, as described inHampel, US. Patent 2,367,771. In this way the bleaching can take placeat pH of 5 or higher and the corrosion of stainless steel equip-- mentbecomes negligible. Although the bath is less acid when formaldehyde isused for activation there is considerable chlorine dioxide evolutionbecause the formaldehyde catalyses its formation. For this reasonformaldehyde activation has not met with commercial acceptance in spiteof its low cost and effectiveness in bleaching.

The new process of this invention avoids the use of corrosive, acidactivated chlorite baths and the unstable, chlorine dioxide-evolving,formaldehyde activated baths described by the prior art. According tothis invention, the cellulosic textile is impregnated with an aqueoussolution containing a reaction product of formaldehyde and certainorganic acid hydrazides. Suitable hydrazides have the formulas: (CONHNHR(CONHNH R(CONHNH and R(CONHNH wherein R is selected from the groupconsisting of hydrogen, saturated hydrocarbon chains andhydroxyl-substituted hydrocarbon chains, R is a saturated hydrocarbonchain interrupted by an oxygen atom and R" is a saturated hydrocarbonchain interrupted by a sulfur atom. Each of the R groups should haveless than about 9 carbon atoms. In the formulas, x is a whole numberless than 4. Examples of some suitable hydrazides include those offormic, acetic, glycolic, adipic, oxalic, diglycolic, tartaric andcitric acids. The use of hydrazides of acids with a higher molecularweight than about that of suberic acid is hampered by waterinsolubility. However, any organic acid hydrazide which is soluble inwater to the extent required can be used. It is surprising that only avery small amount of formaldehyde, in comparison to amounts used in thepast, is efiective when used in combination with these hydrazides. Thereaction of formaldehyde with the hydrazides goes quickly in aqueoussolution to produce compounds whose composition is not definitely known.However, they are water soluble, colorless and stable when used in thedilute solutions of this invention.

The textile containing the aqueous formaldehydehydrazide reactionproduct is then bleached with the aqueous alkali metal or alkaline earthmetal chlorite solution containing from about 0.05% to 2% by weight ofthe chlorite and enough weak acid, such as acetic,

Parts by weight Water 100 Formaldehyde 0.005 to 0.1. Hydrazide 2 totimes the formaldehyde weight.

The textile is then squeezed or dried by gentle warming until itcontains about 30% to 80% by weight of the liquid from the bath. In thisdamp condition the textile is passed into a chlorite bath. The bleachingcan be done by heating the chlorite bath to 80 to 100 C. while the clothresides therein for about 1 to 2 hours, or the cloth can be passedthrough the chlorite bath at room temperature, squeezed until it nolonger drips and then bleached by heating it in a stream box or othersuitable apparatus which provides a hot, humid atmosphere, substantiallysaturated with water vapor, for 1 to 2 hours. Alternatively, the clothfirst can be partially impregnated with the chlorite solution, furtherimpregnated with the hydrazide formaldehyde solution and then heated inthe steam box or other apparatus.

The method of this invention can be used to bleach textiles which areblends of different fibers, for example cotton-rayon or cotton-dacronblends; especially those having 50% or more of cellulosic material. Theterm celulosic textile as used in this specification and claims is meantto include cotton, linen, regenerated cellulose (rayon) and textileblends containing non-cellulosic fibers but having about 50% or more ofcellulosic fibers.

The following examples further illustrate this invention:

Example I A section of white cotton poplin was passed through an aqueoussolution containing 1% by weight of the hydrazide of diglycolic acidO(CH CONHNH and 0.2% by Weight of formaldehyde. It was then squeezedbetween rollers until it contained 82% by weight, based on its ownweight, of the solution. The textile was then partially dried to amoisture content of about 30% by weight based on the weight of thecloth, by heating it at 210 F. for 2 minutes. The cloth was then putinto an aqueous solution containing about 1.6 grams per liter of sodiumchlorite and enough acetic acid to bring the pH to 6.0. After one hourin the bath at 96 C., the cloth was removed, rinsed and dried. Duringthis time the solution gave off no chlorine dioxide. It had an initialreflectance, as measured with a photovolt brightness meter, of 58.4units and a final reflectance of 82.3. With the brightness scale used, adifference of 2 units is discernible by the unaided eye. A second pieceof the cloth bleached in a similar manner, but with nohydrazide-formaldehyde pretreatment, showed a reflectance of only about70 units.

Example 11 A section of white cotton poplin was passed through anaqueous solution containing 0.21% by weight of the hydrazide ofdiglycolic acid and 0.04% by weight of formaldehyde. It was thensqueezed between rollers until it contained 83%, based on its ownweight, of the solution. The cloth was partially dried to a moisturecontent of about 30% by weight based on the weight of the cloth, byheating it at 210 F. for 2 minutes. The cloth was then put into anaqueous solution coni taining about 1.6 grams per liter of sodiumchlorite and enough acetic acid to bring the pH down to 6.0. After onehour in the bath at 96 C. the cloth was removed, rinsed and dried. Ithas a reflectance of 83.0 after the bleaching and only 58.6 before.

Example III An aqueous solution containing 0.6% by Weight ofthiodiglycolic hydrazide, S(CH CONHNH and 0.2% formaldehyde was paddedonto linen to the extent that the cloth retained 70% by Weight, based onits own weight, of the solution. The cloth was then passed into asolution containing 1.9% by weight of magnesium chlorite and enoughacetic acid to bring the pH down to 5.1 at room temperature. The clothpicked up 65% by weight of the bleach solution based on the dry clothweight. The linen was put into a steam box wherein the temperature wasmaintained at 97 C. for 2 hours. After removing the linen from the box,rinsing and drying it, the brightness obtained was 72 compared to anoriginal value of 48.

Example IV A section of mercerized cotton broadcloth was passed througha bath containing 100 parts of water, 0.11 parts of sodium chlorite andenough acetic acid to bring the pH down to 5.3. It was squeezed until itcontained 72% by weight, based on the cloth Weight, of the liquid. Thecloth was then passed through a hath made by mixing 100 parts of water,0.07 part of acetic hydrazide and 0.56 part of formaldehyde. It wasagain squeezed until the total weight of liquids on the cloth was 123%,again based on the cloth weight, and rolled up and placed in an ovenwhere the temperature was 94 C. and the relative humidity about 98%.After 2 hours in the oven the cloth had a brightness or reflectance of77 units compared to an original brightness of 62 units.

What is claimed is:

l. The process for bleaching cellulosic textiles comprising wetting thetextile with two separate, aqueous solutions; one solution containing0.05% to 2.0% by weight of a chlorite of a metal selected from the groupconsisting of alkali metal and alkaline earth metals, acidified to a pHof 5 to 7, and the other solution being prepared by admixing Water,formaldehyde and a hydrazide having a formula selected from the group:(CONHNH R(CONHNH R'(CONHNH and R"(CONHNl-I wherein R is selected fromthe group consisting of hydrogen, saturated hydrocarbon chains andhydroxyl substituted hydrocarbon chains, R is a saturated hydrocarbonchain interrupted by oxygen, R" is a saturated hydrocarbon chaininterrupted by sulfur, each of said R, R and R having less than 9 carbonatoms, and x is an integer less than 4, the proportions by weight being100 parts of water, 0.005 to 0.1 part of formaldehyde and an amount ofhydrazide which is 2 to 10 times the weight of the formaldehyde; andthen heating the textile at C. to C. while it is Wet with saidsolutions.

2. The process of claim 1 wherein the textile is partially impregnatedwith the chlorite solution, then as a second step further impregnatedwith the aqueous hydrazide-formaldehyde solution and then heated at 80C. to 100 C. in an atmosphere substantially saturated with water vaporto effect bleaching.

3. The process of claim 1 wherein the textile is partially impregnatedwith the aqueous hydrazide-formaldehyde solution, then as a second stepfurther impregnated with the chlorite solution and then heated at 80 C.to 100 C. to effect bleaching.

4. The process of claim 3 wherein the aqueous chlorite solution is at atemperature of 80 C. to 100 C. and the textile resides therein untilbleaching is accomplished.

5. The process of claim 3 wherein the textile, while 5 wet with thesolutions, is heated at 80 C. to 100 C.

in an atmosphere substantially saturated with water 2,430,674 HampelNov. 11, 1947 Vapor to effect bleaching. 2,430,675 Hampel Nov. 11, 19476. The process of claim 5 wherein the hydrazide is 2,893,819 Hawkins nJuly 7, 1959 diglycolic hydrazide and the chlorite is sodium chlorite.,9 4,387 Holbrook et a1. Sept. 15, 1959 5 2,904,388 Holbrook et a1.Sept. 15, 1959 References Cited in the file of this patent 2,904,390Holbrook et a1. Sept. 15, 1959 UNITED STATES PATENTS 2,947,700 Waibel Ag- 2, 196

2,367,771 Hampel Jan. 23, 1945 IG ATENTS 2,429,317 Hampel O t. 21, 19 10706,626 Great Britain Mar. 31, 1954

1. THE PROCESS FOR BLENDING CELLULOSIC TEXTILES COMPRISING WETTING THETEXILE WITH TWO SEPERATE AQUEOUS SOLUTION; ONE SOLUTION CONTAINING 0.05%TO 2.0% BY WEIGHT OF A CHLORITE OF A METAL SELECTED FROM THE GROUPCONSISTING OF ALKALI METAL AND ALKALINE EARTH METALS, ACIDIFIED TO A PHOF 5 TO 7, AND THE OTHER SOLUTION BEING PREPARED BY ADMIXING WATER,FORMALDEHYDE AND A HYDRAZIED HAVING A FORMULA SELECTED FROM THE GROUP:(CONHNH2)2, R (CONHNH2)X, R'' (CONHNH2)X AND R"(CONHNH2)X WHEREIN R ISSELECTED FROM THE GROUP CONSITING OF HYDROGEN, SATURATED HYDROCARBONCHAINS AND HYDROXYL SUBSTITUTED HYDROCARBONS CHAINS, R'' IS A SATURATEDHYDROCARBON CHAIN INTERRUPTED BY OXYGEN, R" IS A SATURATED HYDROCARBONCHAIN INTERRUPTED BY SULFUR, EACH OF SAID R, R'' AND R" HAVING LESS THAN9 CARBON ATOMS, AND X IS AN INTEGER LESS THAN 4, THE PROPORTIONS BYWEIGHT BEING 100 PARTS OF WATER, 0.005 TO 0.1 PART OF FORMALDEHYE AND ANAMOUNT OF HYDRAZIDE WHICH IS 2 TO 10 TIMES THE WEIGHT OF THEFORMALDEHYDE; AND THEN HEATING THE TEXILE AT 80*C, TO 100*C. WHILE IT ISWET WITH SAID SOLUTION.